Study tests whether ants can take the heat

Tuesday, 27 November 2012 Bec CrewABC

An increase of just 2°C in the ant's body temperature was the difference between a fully functioning ant and one that was disoriented and constantly falling over (Source: Yinika Perston/University of New England)

Too hot to handle Temperature increases expected due to climate change are likely to change the foraging behaviour of the humble ant, which could have a knock-on effect for global biodiversity, scientists report today.

The common meat ant (Iridomyrmex purpureus) lives in temperate regions of southeastern Australia in such great numbers they have the highest biomass of any animal species in the country.

These ants provide an abundant food source for other species, and play a crucial role in predation, seed dispersal, pollination and nutrient recycling.

Until recently, very little research had addressed how they might be affected by a rapidly changing climate.

Entomologist Nigel Andrew, from the University of New England in Armidale, led a review of more than 1700 studies from 1985 to 2012 into the climate change response of various insect groups.

The review reveals that the response of ants to climate change was significantly under-represented, prompting Andrew and his team conduct their own study.

The team observed how 1500 meat ant workers responded to artificial rises in temperature.

Pushed over the threshold

As ectotherms, ants cannot regulate their internal body heat, so must exchange heat with their surroundings to maintain an optimal temperature.

Andrew and colleagues found that an increase of just 2°C in the ant's body temperature was the difference between a fully functioning ant and one that was disoriented and constantly falling over - their critical thermal limit being around 46°C. At just 4°C above their thermal limit, the ants could not move at all.

High levels of activity on top of the nest were observed up to 42°C, but ants would run faster back to their insulated nest to recover as temperatures continue to rise.

When the ground temperature, which during the hottest part of the day can be 40°C hotter than air temperature, reached 50°C the ants would reduce their activity. At 63°C ground temperature, the foraging stopped altogether.

Changing behaviours

The researchers suggest that rising temperatures could cause meat ants to reduce their daytime foraging, instead foraging at earlier or later parts of the day when they are less efficient, or when their nocturnal predators are more active.

Andrews says other risks to their survival could lie within the nest.

"Are the queen ants digging their nests deeper to deal with the climate? And if the workers are being stressed out, they might not be bringing enough food back. They still need to forage for hundreds of thousands of individuals," says Andrews.

He adds that recovery times for worker ants could also eat into their foraging work and lifespan. "[Their survival] depends on how adaptable they are."

The study concludes, "Ants are one of the most ubiquitous animals in terrestrial ecosystems and play crucial roles in ecosystem functioning on all continents except Antarctica."

"Therefore understanding how ants will respond to climate variation is of fundamental importance in understanding, and sustaining, global biodiversity."